> ## Documentation Index
> Fetch the complete documentation index at: https://private-7c7dfe99-framing-web-ui.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# materialized_views_* session settings

> ClickHouse session settings in the materialized_views_* generated group.

export const VersionHistory = ({rows = []}) => {
  if (rows.length === 0) {
    return null;
  }
  const headers = ["Version", "Default value", "Comment"];
  const border = "1px solid rgba(128, 128, 128, 0.3)";
  const cell = {
    border,
    padding: "0.25rem 0.5rem",
    textAlign: "start",
    verticalAlign: "top"
  };
  return <details className="not-prose" style={{
    border,
    borderRadius: "0.5rem",
    margin: "0.5rem 0",
    padding: "0.5rem 0.75rem",
    fontSize: "0.8125rem",
    lineHeight: "1.125rem"
  }}>
      <summary style={{
    cursor: "pointer",
    fontWeight: 600,
    opacity: 0.72
  }}>
        Version history
      </summary>
      <table style={{
    borderCollapse: "collapse",
    width: "100%",
    margin: "0.5rem 0 0"
  }}>
        <thead>
          <tr>
            {headers.map(header => <th key={header} style={{
    ...cell,
    fontWeight: 600,
    opacity: 0.72
  }}>
                {header}
              </th>)}
          </tr>
        </thead>
        <tbody>
          {rows.map((row, row_index) => <tr key={row.id ?? row_index}>
              {(row.items ?? []).map((item, item_index) => <td key={item_index} style={{
    ...cell,
    overflowWrap: "anywhere"
  }}>
                  {item?.label}
                </td>)}
            </tr>)}
        </tbody>
      </table>
    </details>;
};

export const SettingsInfoBlock = ({type, default_value, changeable_without_restart}) => {
  return <div className="not-prose" style={{
    display: "flex",
    flexWrap: "wrap",
    alignItems: "baseline",
    columnGap: "0.5rem",
    rowGap: "0.125rem",
    margin: "0.375rem 0",
    fontSize: "0.8125rem",
    lineHeight: "1.125rem"
  }}>
      <div style={{
    fontWeight: 600,
    opacity: 0.72
  }}>Type</div>
      <div style={{
    overflowWrap: "anywhere"
  }}>{type}</div>
      <div style={{
    fontWeight: 600,
    opacity: 0.72,
    marginInlineStart: "0.5rem"
  }}>Default</div>
      <div style={{
    overflowWrap: "anywhere"
  }}>{default_value}</div>
      {changeable_without_restart && <div style={{
    fontWeight: 600,
    opacity: 0.72,
    marginInlineStart: "0.5rem"
  }}>
          Changeable without restart
        </div>}
      {changeable_without_restart && <div style={{
    overflowWrap: "anywhere"
  }}>
          {changeable_without_restart}
        </div>}
    </div>;
};

These settings are available in [system.settings](/reference/system-tables/settings) and are autogenerated from [source](https://github.com/ClickHouse/ClickHouse/blob/master/src/Core/Settings.cpp).

<h2 id="materialized_views_ignore_errors">
  materialized\_views\_ignore\_errors
</h2>

<SettingsInfoBlock type="Bool" default_value="0" />

If enabled, exceptions thrown while pushing data to a dependent materialized view (in its `SELECT` or in the inner table sink) are logged as a warning and the `INSERT` statement succeeds. If disabled (default), such an exception propagates and the `INSERT` statement fails.

This setting controls only error reporting. It does not roll back a write to the source table, and it does not guarantee whether the original block has already been committed to the source table when an error occurs in a dependent view's pipeline. When disabled (default), the `INSERT` fails on a view error — retry it with insert deduplication (`insert_deduplicate`, `deduplicate_blocks_in_dependent_materialized_views`) for exactly-once delivery to the source table and all dependent views. When enabled, the `INSERT` reports success despite partial delivery to failing views and their downstream chains; use this only when source-table writes must not be blocked by view-side problems (for example, `system.*_log` tables). See the `CREATE VIEW` docs for full semantics.

<h2 id="materialized_views_populate_atomically">
  materialized\_views\_populate\_atomically
</h2>

<SettingsInfoBlock type="Bool" default_value="1" />

<VersionHistory rows={[{"id": "row-1","items": [{"label": "26.8"},{"label": "1"},{"label": "New setting that makes plain `CREATE MATERIALIZED VIEW ... POPULATE` locally atomic: existing data is snapshotted and the view is subscribed to new inserts together, under a brief exclusive lock on the source, so rows inserted through the same server are neither missed nor duplicated. The guarantee covers the local insert path only - inserts arriving on another replica or through a distributed write are outside the cut - and it requires a source that can provide a pinned snapshot (the `MergeTree` family and `Memory`); other sources, as well as `CREATE OR REPLACE` \/ `REPLACE`, keep the legacy non-atomic population. Set to `false` for the legacy non-atomic behavior everywhere."}]}]} />

Make `CREATE MATERIALIZED VIEW ... POPULATE` atomic: the view is subscribed to new inserts of the source table and a snapshot of the existing data is taken together, under a brief exclusive lock on the source table, so that every row inserted concurrently with the population is delivered to the view exactly once (neither missed nor duplicated). The (possibly long-running) population then reads the pinned snapshot without holding any lock.

This is local insert-path atomicity: the exclusive lock only serializes with inserts that acquire this source table's storage lock on the same server, so the exactly-once guarantee covers inserts arriving through this server. It is not a cluster-wide guarantee - rows inserted on another replica of a `ReplicatedMergeTree` source, or through a distributed write path (for example, into a `Distributed` table or via `ON CLUSTER`), concurrently with the population can still be missed or duplicated.

This requires the source table to support reading a pinned point-in-time snapshot (the `MergeTree` family and `Memory`). For any other source (a view, `Distributed`, `Merge`, the `Log` family, or a table not in an `Atomic` database) the population falls back to the legacy, non-atomic behavior (recorded in the server log): existing data is read with a separate, non-coordinated snapshot, so rows inserted during the population can be missed or duplicated. Set this setting to `false` to force the legacy behavior for all sources. Applies to plain `CREATE MATERIALIZED VIEW` only; `CREATE OR REPLACE` / `REPLACE` always use the legacy non-atomic population, and so does a view created in a `Replicated` database (where `POPULATE` requires `database_replicated_allow_heavy_create`), because a failed population could not be rolled back consistently on all replicas there.

<h2 id="materialized_views_squash_parallel_inserts">
  materialized\_views\_squash\_parallel\_inserts
</h2>

<SettingsInfoBlock type="Bool" default_value="1" />

<VersionHistory rows={[{"id": "row-1","items": [{"label": "25.10"},{"label": "1"},{"label": "Added setting to preserve old behavior if needed."}]}]} />

Squash inserts to materialized views destination table of a single INSERT query from parallel inserts to reduce amount of generated parts.
If set to false and `parallel_view_processing` is enabled, INSERT query will generate part in the destination table for each `max_insert_thread`.